Phosphorus-tin oxide oxidative dehydrogenation catalyst

ABSTRACT

THE ACTIVITY OF A CATALYST USEFUL FOR THE OXIDATIVE DEHYDROGENATION OF OLEFINS COMPRISING OXIDES OF PHOSPHORUS AND TIN IS IMPROVED BY TREATING THE CATALYST WITH SUPERHEATED STEAM TO PRODUCE A CATALYST HAVING A SURFACE AREA OF WHICH AT LEAST 2 M.2/G. IS COMPRISED OF PORES HAVING DIAMETERS OF AT LEAST 700* A.

United States Patent "ice US. Cl. 252435 9 Claims ABSTRACT OF THEDISCLOSURE The activity of a catalyst useful for the oxidativedehydrogenation of olefins comprising oxides of phosphorus and tin isimproved by treating the catalyst with superheated steam to produce acatalyst having a surface area of which at least 2 m. /g. is comprisedof pores having diameters of at least 700 A.

This is a continuation of application Ser. No. 39,544, filed May 21,1970, now abandoned.

This invention pertains to catalyst compositions.

In one of its more specific aspects, this invention pertains to themazimization of activity of phosphorus-tin oxide andlithium-phosphorus-tin oxide catalysts having porous structures.

Phosphorus-tin oxide and lithium-phosphorus-tin oxide catalysts areemployable in the oxidative dehydrogenation of organic compounds, suchas alkenes, alkadienes, cycloalkenes, alkylpyridines and alkyl aromaticsto produce unsaturates such as 1,3-butadiene, isoprene, styrene and thelike.

A method has now been discovered for increasing the catalytic activityof these catalysts. Simultaneously therewith, there has been discovereda novel catalyst composition for oxidatively dehydrogenating organiccompounds.

According to the method of this invention, there is provided a processfor increasing the activity of a phosphorus-tin oxide-containingoxidative dehydrogenation catalyst which comprises treating the catalystto impart to the catalyst a surface area of which at least 2 m. g. is inpores having a minimum diameter of 700 A.

Also, according to this invention there is provided a novel catalystcomposition and a process for the oxidative dehydrogenation of organiccompounds which employs that catalyst.

Accordingly, it is an object of this invention to provide an improvedoxidative dehydrogenation catalyst.

It is another object of this invention to provide a process for treatinga catalyst, the result of which is to provide a catalyst which producesincreased yields of oxidatively dehydrogenated products.

This invention applies to those catalysts employed for oxidativedehydrogenation, those catalysts comprising phosphorus, tin, a metal ofGroup Ia or Ila, and oxygen. The presence of the Group Ia and Ila metalis preferred but optional. The catalyst contains from about 0.1 to about16 weght percent phosphorus and from about 15 to about 75 weight percenttin. If the Group 10: or Ila metal is present, it is present in anamount up to about 5 weight percent and the metal is preferably lithium,the remainder being, substantially, combined oxygen.

The method of this invention pertains to that catalyst,

3,810,844 Patented May 14, 1974 and its use, as defined and disclosed inapplication Ser. No. 810,831 filed by George I. Nolan and Robert J.Hogan on Mar. 26, 1969, now abandoned.

In general, such catalysts are prepared by combining solutions ofphosphorus and tin compounds under conditions suitable to produce asolid which is recovered and calcined.

For example, a catalyst can be prepared by adding 17.2 lbs. of SnCl -5H0 in 4 gal. of deionized water, adding 3.7 lbs. of percent H PO to 2gal. water, combining these solutions, adding NH OH solution (7 litersof 58 percent N'H OH in 15 gal. water), until the pH is 3.5, aging theprecipitate 6 or more hours, filtering, washing to remove essentiallyall of the chlorine, drying, forming into fli-inch tablets, andcalcining at 1100 F. for 3 hours.

To produce the lithium-containing catalyst, the abovepreparedphosphorus-tin oxide tablets can be impregnated with a sufiicientquantity of an aqueous solution of lithium nitrate to give 1.5 weightpercent lithium in the finished catalyst after calcination in air for 2hours at 1100 F.

Catalysts of the phosphorus-tin oxide type are employed in oxidativedehydrogenation by contacting the dehydrogenatable organic feed with thecatalyst, and with steam and a free oxygen-containing gas. Preferably, amixture of the dehydrogenatable organic feed, steam and freeoxygen-containing gas is contacted with the catalyst.

The contact is made at temperatures of from about 700 F. to above 1300"E, at pressures of from about 0.05 to about 250 p.s.i.a. and at ahydrocarbon GHSV of from about 50 to about 5000. The oxygen to gaseousorganic feed volumetric ratio can be from about 0.1 to l to about 3 to1, and the steam ratio can be from about 0.1 to about 50 volumes pervolume of organic vapor.

The catalyst improvement method of the present is employed to adjust thecatalyst to desired surface area, a portion of which is contributed bypores having diameters no less than a specified size. Adjustment of thecatalyst can be made at any stage within the catalyst preparationprocedure at which point the desired surface area effect can be producedwithout being substantially reduced by a subsequent step. For example,it can be practiced during drying, during calcining, while pelleting, orafter the finished catalyst, in whatever form it is employed, is packedin a bed.

The method of the present invention produces a catalyst having a surfacearea in which at least 2 m. /g. is in pores having a minimum diameter of700 A. It is preferable that the entire surface area of the catalyst becomprised of pores having substantially a diameter of 700 A; or, it ispreferable that the entire surface of the catalyst be comprised of poreshaving a minimum. diameter of 700 A. and a maximum diameter of 800 A. Inpractical situations, however, the range of pore sizes probably will begreater than that ideally desired.

The catalyst, when produced by the usual prior art methods ofproduction, will not necessarily possess such surface area-pore sizedistribution. However, this surface area configuration can be attainedby a number of methods, any of which is satisfactory. -In general, asatisfactory method acts to collapse the intercellular walls betweensmall pores to form larger pores of 700 A. or larger, and/or to form newpores of this size, and thus to provide the proper combination ofsurface area and pore diameter.

r e I Any method which produces the desired surface areapore sizerelationship can be employed. Steaming with superheated steam tomaintain the catalyst between about 1000 F. and 1700" F., preferablybetween 1300 F. and 1600" F. for a time sufiicient to produce thedesired increase in surface area and activity, will sufiice. Anyconvenient pressure can be used for the steam treatment.

Relatedly, the method of this invention can be carried out by heatingmoisture-carrying gases in contact with the catalyst to produce steamwithin the catalyst pores and to raise the catalyst to the temperaturesspecified.

The method of this invention will be illustrated using the steamingprocedure without meaning to limit the invention thereto.

A phosphorus-tin oxide catalyst containing 10 percent phosphorus wasprepared in the manner previously described in which the precipitate hadbeen washed, dried and formed into At-inch pellets which were calcinedfor 3 hours at 1100 F.

This catalyst, referred to hereinafter as Catalyst No. 1, was employedin its as prepared condition for the oxidative dehydrogenation ofbutene-2. Other samples of this same catalyst were steamed at varioustemperatures in accordance with the method of this invention to attainthe desired surface area configuration. All of the samples were thenemployed for the oxidative dehydrogenation of butane-2.

In all the oxidative dehydrogenations, butene-Z was passed in asingle-pass operation in contact with air, as the oxygen-containing gas,and with steam at atmospheric pressure and at temperatures indicated inTable I. Steam to butene ratios were maintained as constant as possibleand ranged from 16.7 to 18.2. The butene-2 space velocity was 300 GHSV,the airzbutene-Z ratio was 4:1, and the pressure was atmospheric.Results for the No. 1 Catalyst in the unsteamed condition and for eachof the samples of the No. 1 Catalyst in the steamed condition were asshown in Table I.

TABLE I.--GATALYST NO. 1

Sample 1 2 3 4 5 Steam treatment, I for 16 hrs. None 1, 250 1, 350 1,450 1, 550 Surface area in pores larger than 700 A., mfl/g 4.2 1. 5 2. 63. 8 5. 2 Total surface area, mJ/g 28 26 25 22 10 Dehydrogenationresults:

After min. at 900 F.:

Yleld 46 40 48 59 63 Reaction rate 6. 2 4. 0 6. 1 9. 1 12. 5 Modivity,percent 97 98 98 98 99 After 15 min. at 1,000 F.:

Yield 52 47 54 70 75 Reaction rate 7. 1 5. 6 8. 0 13. 4 18. 3 Modrvity,percent 96 98 97 97 97 In the above table, Yield is defined as moles ofbutadiene produced per 100 moles of butene-Z in the feed per pass.

Reaction Rate is defined as moles of butadiene produced per liter ofcatalyst per hour, at a butadiene yield of 50 percent.

Modivity" is selectivity based upon the gaseous products, namely, C to Chydrocarbons, carbon dioxide, and carbon monoxide.

Pore volume and surface area were measured by mercury intrusion at15,000 p.s.i.g. with an Aminco digital readout porosimeter (AmericanInstrument Company, inc.). Total surface areas were measured by nitrogenadsorption.

The above data illustrate the operability of the method of thisinvention. They also indicate that the initial effect of steam was toreduce that amount of surface area contributed by large pores (that is,pores having diameters larger than 700 A.) and also to reduce thereaction rate. However, with increasing steaming temperature, surfacearea in large pores was increased as was the yield and reaction rate. Asthe steaming temperature was increased further, a further increase inarea in large pores as well as in yield and reaction rate wasexperienced at least up to a temperature of 1550 F.

A catalyst was prepared by coprecipitating sufiicient SnCl, and H POwhich, after washing, drying, forming into Az-inch tablets and calciningthree hours at 1100 F., contained 10 weight percent phosphorus. Thesetablets were impregnated with sufiicient LiNO solution to provide, afteranother calcination, 1.5 weight percent lithium based on thephosphorus-tin oxide composition.

Several samples of the above-prepared catalyst were subjected to severallevels of steam treatment and then tested for oxidative dehydrogenationactivity under the same dehydrogenation conditions described above. Thesteaming conditions and results of the dehydrogenation tests are shownin the following table:

TABLE II.-CATALYST NO. 2

The above data illustrate the operability of the method of thisinvention in respect to the lithium-containing catalyst. Again, as inthe case of Catalyst No. 1, with an increase in steaming temperature,both the yield and modivity increased appreciably over those values atthe lower steaming temperature.

Inasmuch as the unsteamed catalyst can have surface areas in excess of35, it is possible that the nitrogen surface area of the steam catalystcan be above 35 as an upper limit and, as the total surface area becomesrepresented in pores of 700 A., a lower surface area of about 6.

While no attempt is made to explain the invention, it would appear thatother factors, not specifically related to surface area or porediameter, are also affected by the steaming embodiment of this inventionsince, in the initial stages of steaming, there is an actual decrease inthe surface area contributed by pores having a diameter of at least 700A. but the catalyst yield and reaction rate are, nevertheless, actuallyincreased when considered in relation to the amount of surface availablein these pores. While the surface area-pore diameter relationship is apertinent factor in the improvement of catalyst activity, some of theseother factors, which are affected by the steaming method of thisinvention and which relate to the intrinsic activity, could be catalystskin configuration, pore volume, skeletal density, tablet volume andcassiterite or crystalline tin oxide content. Seemingly, then, in theabove tests, the intrinsic activity of the catalyst was affected bysteaming at 1250" F. Further increases in steaming temperature may havehad, up to the point of possibly excessive treatment, little additionaleffect on this intrinsic activity while making more surface areaavailable in pores larger than 700 A. than were available in thatcatalyst steamed at 1250 F. The net result was an increase in catalyticactivity up to a steaming temperature of about 1600" F.

It will be evident from the foregoing that various modifications can bemade to the method of this invention. Such, however, are considered asbeing within the skill of the art.

What is claimed is:

1. A process for producing an oxidative dehydrogenation catalystcomprising contacting (a) a calcined composite consisting essentially of0.1 to about 16 weight percent phosphorus, 15 to about 75 weight percenttin, 0 to about 5 weight percent lithium, and the remainder beingsubstantially combined oxygen with (b) superheated steam sufficient toproduce a catalyst having a surface area of which at least 2 m./ g. iscomprised of pores having diameters not less than 700 A.

2. A process according to claim 1 wherein the contacting is at atemperature between abmii 1300"v and 1600 F.

3. A process according to claim 1 'wherein said steam is generatedwithin the pores of the catalyst.

4. A process according to claim 1 wherein the porosity of the catalystis adjusted by steam treatment sufficient to produce a catalyst surfacearea comprised of an increased portion of pores having diameters between700 A. and 800 A. as compared to the catalyst prior to said treatment.

5. A process according to claim 1 wherein a catalyst is adjusted to havea total surface area of from about 6 to about 35 mF/g. of which totalfrom about 2 mF/g. tov

about 5.2 m./ g. is comprised of pores having a diameter not less than700 A. a 1 p 6. A process according to claim 5 in which said catalysthas a total surface area of about 10 mfi/ g. of which total about 5.21119/ g. is comprised of pores having a diameter greater than 700 A.

7. The product of the process of claim 2. 8. The product of the processof claim 1. 9. The product of the process of claim 6.

References Cit-ed UNITED STATES PATENTS 15 PATRICK P. GA-RVIN, PrimaryExaminer US. Cl. X.R.

262-437; 260-668 D, 669 R, 680 E, 290 V

